The digital zooming thing

Or more accurately the “post-shoot digital zooming thing”. Or the “making use of 24MP” thing.

The premise is that with a high resolution sensor you can crop quite a small portion out of the full frame and still have a reasonably sharp image to present. This is the opposite of demonstrating why high MP sensors aren’t any advantage once the picture is reduced to ‘normal’ size. Let’s see how it works.

The camera: Sony a6000 with 24 MP sensor. The lens: Pentax Super Takumar 50mm f1.4 (the sharpest lens I own). The subject: a dollar store decoration cardinal standing in for a real bird because it won’t fly away while I’m photographing it. The distance: approximately 50 feet.

This is one picture cropped four ways and ending up at 1500 x 1000 each time.

Full frame, shrunk down to size. Bird is a red spot.

 

One quarter frame: 3000 x 2000 crop, centered on the bird. Still a red spot.

 

Approximately one eighth crop. You can almost tell it’s a bird.

 

One sixteenth. This is a 1500 x 1000 segment of the full frame.

As you can see, 1/16 of the full frame is about the maximum limit. It is already “soft” and it still doesn’t reveal the bird very well. Of course 50mm isn’t much focal length (about 75mm equivalent) so for actual birding a longer lens would do better. What we’re studying here is the cropping effect on resolution. This size is slightly larger than my ‘normal’ image presentation, and it is noticeably soft even to my eyesight. Applying the “unsharp mask” doesn’t help.

So what do we learn? We learn there is no substitute for being close to the subject in the first place, whether in actual distance or by use of telephoto lens (which adds its own problems due to looking through increased atmosphere). You can make use of some digital zooming this way, but don’t expect it to be a substitute for multiples of focal length.

By the way, this is the third experiment I did like this. I’m using the examples from this one because they present the best demonstration with the best lens. I have also done it with the 135mm Vivitar, with similar results. If anything the longer focal length adds to the drop-off in sharpness because longer lenses tend not to be as sharp. In other words the digital cropping will not only magnify the image, but any flaws in it as well.

The third experiment utilized the Soligor 85-205mm zoom and a Pentax 2X extender as I was trying variations to see how having an actual long lens would affect the field of view. Or to put it simply, to see if buying the 50-210mm Sony zoom would give enough focal length to make birding pictures possible. The result was “no”. Disregarding the softness of the lens, the field of view was not magnified sufficiently to make for good identification of the bird.

From 60 feet, taken with the Soligor at 205mm (307mm equivalent).
Same spot, but this taken with the Nikon at 1440mm equivalent.

As you can see, for birding a long focal length is desirable because you probably won’t be able to get close to them physically. In fact having the wide zoom range is valuable because you never know how far away you will be when you spot something. This is why I like the Nikon P610, although it needs a faster zoom control and better viewfinder. Hence my recent reference to the desirability of an actual DSLR with a tiny 1/2.3 sensor. But that’s not going to happen. Nor will any manufacturer come up with a digital “sport finder”: a wider frame of view with a centered square indicating the actual image area so small objects can be spotted more easily and brought in close. Perhaps some camera has this, but I haven’t seen it.

I’m still at sixes and sevens about the Sony a6000. It is a very good camera and does produce excellent results. For the most part it’s easy to use and has great lens adaptability. There are only a few flaws, and I can’t quite decide if they are too much to put up with. I think I need to use it more before determining whether it’s worth sinking additional money into or selling it off for whatever I can get.

3 thoughts on “The digital zooming thing

  1. Hi Marc, just had this new post here in the UK…. have a look at my response to your previous post… doing a bit of quick maths… or math as they say in the US..lol… the crop factor on the Q/Q10 would take that 135mm you have up to a massive 742mm which would be plenty for your birding…. I would of thought… but as I said in the earlier one.. Have a word with Dan about the Q range, they are a very well devolped underated camera in my view… the only downside that may be an issue for you is the actual size of the camera… especially the Q10 which is a real street photographers dream as it is literally small enough to fit in a coat pocket but it also makes it ideal for taking outside at any time,… BR Lynd..

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    1. Thanks for the suggestion, Lynd. Strangely enough I had considered the Pentax Q, but for some of the things you mention it’s not suitable for me. The small size for one thing, as well as the limited lenses owing to being discontinued. Mostly there’s the problem of the EVF which I have a hard time seeing now, and the prices … OUCH! Ego-Bay has banned me for no reason so I don’t get to have fun there.
      It would be nice to have a 4/3 sensor camera like my E410 but one with greater resolution – and longer lens.
      It’s sad that the Sony is such a good camera and yet has drawbacks for my use. Maybe I need to change the nature of my art.

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  2. Hi Marc, All noted on the comments…and yes the Q range does have its issues like they all have but the biggest issue is the size… and yes I never gave it a thought about the evf and your sight problems… sorry….. but please for one reason or another… do not change the the nature of your art…. oh and also… some of those moon shots you have are unbelievable… they really are… Hope that the recovery is coming along as predicted… take care during these fraught times… Kind regards… Lynd

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